STALL,TIP-IN HES. AND/OR STORED ENGINE CODES (PROMS)

VEHICLES AFFECTED: 1987-88 J/A/L,1988 W

THIS BULLETIN HAS BEEN REVISED TO ADD ADDITIONAL STEPS TO CLEAN THE THROTTLE BODY UNDER 3C AND INFORMATION UNDER 3I.

Some customers with an engine/vehicle combination listed below

1987 J-Car With a 2.8L Engine (VIN Code W) 1988 W-Car With a 2.8L Engine (VIN Code W) 1987-88 A and L Models With a 2.8L Engine (VIN Code W)

may comment that they have experienced one or more of the following conditions:

A cold start stall or sag,

A decel stall

A tip-in hesitation

A check engine light with stored Codes 23, 25, 33, 34 or

An engine speed flare during a declutch operation with a manual transmission equipped vehicle.

These conditions may be attributed to a number of components/interactions. In the interest of simplifying diagnosis and repair, the following procedure has been developed to reduce system sensitivity, thereby addressing a variety of potential causes simultaneously.

If a customer comment concerning an occasional engine stall or a drive hesitation is received, and/or a stored Code 33 or 34 is found, then complete the following procedure:

1. Perform diagnostic procedures per Section 6E of the Service Manual, and correct any faults except for Codes 33, 34, 23 or 25. If the diagnostics indicate the Mass Air Flow (MAF) is to be replaced or a Code 33 or 34 is present, DO NOT REPLACE THE MAF SENSOR! Proceed to Step #3. If a Code 23 or 25 is present, go to Step #2 below. PROCEED TO STEP #3 ONLY IF NORMAL DIAGNOSTIC CHECKS DID NOT IDENTIFY A CAUSE FOR THE CUSTOMER CONCERN.

2. If a Code 23 or 25 is stored, perform the model year diagnostics for the Manifold Air Temperature Sensor (MAT). If the diagnostics indicate that the MAT is faulty and replacement is required, replace the combination MAT/MAF sensor. Proceed to Step #3.

3. Install a new MEM-CAL into the Engine Control Module (ECM) per instructions below. The new MEM-CAL is available from CANSPO. See attached service part number chart. Install the identification label package to the ECM access door and to the left shock tower per label kit, P/N 10154725 instructions.

IMPORTANT: The new MEM-CAL to be installed does not need or use the existing MAF signal; however, it does need and use the MAT signal.

A). Pull the underhood ECM continuous power fuse or disconnect the battery and leave it disconnected for at least 10 minutes.

B). Remove MAF relay, if applicable, and discard. Tape up connector to prevent water intrusion.

C). Remove current MEM-CAL and install a new service MEM-CAL. Clean throttle body I.D. bore in the area behind the throttle plate. Use a shop towel with GM Top Engine Cleaner P/N #1052626, or AC-Delco Carburetor Tune-Up Conditioner, P/N #X66-A, or equivalent not containing Methyl Ethyl Ketone.

D). Restore the battery power and place air conditioning controls (if equipped) in the "off" position.

E). Firmly apply the parking brake and block the drive wheels. Start the engine, and shift the transaxle to "drive" for automatics or "neutral" for manuals.

F). Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

G). Turn the ignition key to the "off" position for at least 5 seconds.

H). Start the engine, and shift the transaxle to "drive" for automatics or "neutral" for manuals.

I). Allow engine to run for at least 5 minutes. Install Tech 1 Scanner tool, CAMS of equivalent. Program into Scan-Tool '89 model year.

With engine stabilized and in closed loop, the IAC motor position values should be between 9-20 counts for a desired RPM of 700 (Auto. Trans. and 850 Manual Trans.). If not, the adjustments may be tailored as follows, by adjusting the minimum air rate screw.

- More throttle valve opening - lower IAC valve counts

- Less throttle valve openings = higher IAC valve counts

IMPORTANT: Throttle angle must be equal to zero.

After a MEM-CAL replacement, the 1987-88 2.8L Speed Density Engine Driveability and Emissions Manual, ST399-87/88 SDM, must be used for Driveability and Emissions Diagnostics. Until the supplement is available, use 1989 model year for scanner-type diagnostics. For additional information, call the GM Technical Assistance Centre.

Use applicable Labour operations and claim total hours (time plus additional time) as follows:

A-Car = 1.0 Hour

J-Car = 0.9 Hour

1987 L-Car = 0.9 Hour

1988 L-Car = 0.8 Hour

W-Car = 0.8 Hour

Add 0.1 hour to the above times to adjust minimum idle.

MEM-CAL SELECTION CHART - SERVICE PART NUMBERS

IMPORTANT: MEM-CAL MUST BE ORDERED WITH LABEL KIT, P/N 10154725

MODEL MODEL CAR* EMISSION MEM-CAL SCANNER BROADCAST YEAR TYPE DIV. TRANS. CONFIG. P/N I.D. CODE

87-88 L 1 AUTO 3-SPD. FED 16140337 0341 ASMJ 87 J 1,3,6 AUTO 3-SPD. FED 16140342 0381 ASMN 87 A 1,2, AUTO 3-SPD. FED 16140350 0461 ASMY 88 A 1,2 AUTO 3-SPD. FED 16141555 1561 ASUZ 87-88 A 3.4 AUTO 3-SPD. FED 16140346 0421 ASMT 88 W 2,3,4 AUTO 4-SPD. FED 16141562 1621 ASWH 87 A 1,2 AUTO 4-SPD. FED 16140352 0471 ASMZ 88 A 1,2 AUTO 4-SPD. FED 16141556 1571 ASWA (NOT STE)

88 A 2 AUTO 4-SPD. FED 16141557 1581 ASWB (WITH STE) 87-88 A 3,4 AUTO 4-SPD. FED 16140347 0431 ASMU 87 J 1,3,6 MAN. 5-SPD. FED 16148227 8261 ATZA 87-88 A 1,2 MAN. 5-SPD. FED 16140355 0501 ASNC 87-88 L 1 MAN. 5-SPD. FED 16148340 8341 ATZD 88 W 2,3 MAN. 5-SPD. FED 16148222 8241 ATYY

1 =CHEVROLET 2 =PONTIAC 3 =OLDSMOBILE 4 =BUICK 6 =CADILLAC

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.